static string constants in class vs namespace for constants [c++]

Question

I want to declare string constants that will be used across various classes in the project. I am considering two alternatives

Option 1:

#header file 
class constants{
    static const string const1;
};

#cpp file

const string constants::const1="blah";

Option 2:

#header file 
namespace constants{
    static const string const1="blah";
};

Just wondering what would be a better implementation.

Already looked at

Where to store Class Specific named constants in C++

Where to put constant strings in C++: static class members or anonymous namespaces

---

UPDATE:

Option 3:

Based on the suggestions from "potatoswatter" and "sellibitze" i currently have the following implementation?

#header file
namespace constants{
    extern const string& const1(); //WORKS WITHOUT THE EXTERN  ***WHY***
};

#cpp file
namespace constants{
   const string& const1(){static string* str = new string ("blah"); return *str;}
}

I'm including the header file where i need to use the constants. Are there any major cons of this implementation?

Answer 1

^{Update 2 years later:}

Every global accessible by more than one source file should be wrapped in an inline function so the linker shares the object between the files, and the program initializes it properly.

inline std::string const &const1() {
    static std::string ret = "hello, world!";
    return ret;
}

The inline function is implicitly extern and may be wrapped in a named namespace or a class, if you like. (But don't use a class just to hold static members, as namespaces are better for that. And don't use an anonymous namespace as that would defeat the linker, and each source would see a different std::string object.)

Answer 2

All answers that resort to std::string run the risk of dynamically allocating memory for a string literal which is going to remain constant throughout the lifetime of the program (and the binary), so they should be avoided.

sellibitze's answer comes close but it has the problem of declaring it once and then defining it elsewhere, which I don't find elegant and is more work. The best way would be

namespace constants {
    const char * const blah = "blah!"
    const char * const yada = "yada yada!"
}

This is solution is discussed further here.

Answer 3

Neither. I'd go with this:

// header file
namespace constants {
extern const char const1[];
}

// cpp file
namespace constants {
extern const char const1[] = "blah";
}

The header file contains a declaration of const1 with incomplete type but convertible to char const* and the cpp-file contains a definition of the character array with external linkage. There is no dynamic initialization like you have with std::string. So, that's a plus, IMHO.

Answer 4

Option 1 achieves the same as Option 2, but in a messier way.

If you're going to use a class that just has static members, especially for global access/constants, use a namespace.